1. Field of the Invention
The present invention relates to a semiconductor device, a method of forming a bump electrode of a semiconductor device, a method of packaging a semiconductor device, a chip carrier tape, a display device and an electronic printing device incorporating a semiconductor device having a bump electrode formed by the present method.
2. Description of the Related Art
A well-known method for forming a bump electrode of a semiconductor device uses a wire bonding technique. With reference to FIG. 14, a torch such as an electric torch (not shown) is opposed to the leading end of a wire 3 made of, for example, gold, copper, solder or aluminum which is passed through a capillary 1, and a spark is generated between the wire 3 and the electric torch, thereby forming a ball at the leading end of the wire 3. Subsequently, the ball is pressed against an electrode of a semiconductor (e.g., a single crystal silicon) substrate 4 (which can include, for example, an aluminum film 6 and a passivation film 5 thereon) to be joined to the wire 3 by lowering the capillary 1 as shown in FIG. 15. Ultrasonic waves are applied to the edge portion of the electrode terminal to secure the ball to substrate 4. Heat from an unillustrated heater block is also transmitted to the bump electrode 7 through the semiconductor substrate 4. Such heat fuses and fixes the bump electrode 7 onto the electrode of the semiconductor substrate 4. Then, as shown in FIG. 16, the wire 3 is held by closing a clamp 2 and torn by simultaneously raising the wire 3 and clamp 2, so that a bump electrode 7 is formed on the electrode of the semiconductor substrate 4. For an example of this conventional bump electrode formation method see, for example, Japanese Laid-open Patent No. 49-52973.
In the above described method, a portion 8 of the metal wire having a length of from about 10.about.40 .mu.m remains as a part of the bump electrode due to the growth of crystal grains in the metal wire arising from the heat of the ball when the capillary 1 and wire 3 are raised. Therefore, the height of the bump electrode becomes uneven. FIG. 17 is a photograph of a bump electrode made by this prior art process. Furthermore, the leading end of the bump electrode (the part containing portion 8) is acutely shaped, and thus the bump electrode cannot be brought into uniform contact with other electrodes, terminals, or contacts. These problems make it impossible to obtain good electric continuity, resulting in inconveniences, such as defective continuity and short circuits between electrodes.
In "Chip-On Glass Mounting Technology of LSIs for LCD Module", IMC 1990 proceedings, Tokyo, May 30-Jun. 1, 1990, Yoshihiro Bessho et al disclose applying a conductive adhesive to stud bumps so that LSIs can be bonded to electrode terminals on an LCD panel. Prior to applying the conductive adhesive to the stud bumps, the stud bumps are pressed by a flat surface to level the bumps on the LSI chip. See step (2) on page 187.